Electronic dryness control



Filed May 28, 1968 A. J. ELDERS ELECTRONIC DRYNESS CONTROL 2Sheets-Sheet 1 I'NVENTOR. 41 Wu J 5Q 0645 ATTORNEYS Aug. 4, 1970 FiledMay 28, 1968 A. J. ELDERS ELECTRONIC DRYNESS CONTROL 2 Shee ts-Sheet 2INVENTOR. 44 w/v J. fla /es ATTORNEYS United States Patent O 3,522,660ELECTRONIC DRYNESS CONTROL Alvin J. Elders, Stevensville, Mich.,assignor to Whirlpool Corporation, Benton Harbor, Mich., a corporationof Delaware Filed May 28, 1968, Ser. No. 732,767 Int. Cl. F26b 19/00 US.CI. 3445 6 Claims ABSTRACT OF THE DISCLOSURE A dryness control for alaundry machine which results in safe and consistent performanceregardless of grounding of the machine, the way the plug of the servicecord is inserted in an electrical outlet or the existence of exposedmetal parts in the dryer drum. An electrical resistance is connectedbetween one of the power input leads and a moisture sensing electrodewhich senses dryness of the fabric within the dryer.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesin general to dryer apparatus and more specifically to control circuitryfor dryness controls in fabric dryers.

Description of the prior art The prior art in regard to which thepresent invention is an improvement is exemplified by the pendingapplication of the assignee of the present application, namely, U.S.Ser. No. 548,678, filed May 9, 1966, wherein is disclosed a dryer havingelectrodes for sensing the predetermined degree of dryness of thefabrics in the treatment zone of the machine.

SUMMARY OF THE INVENTION The present invention relates to a circuit fora fabric dryer laundry machine having moisture sensing electrodes and atimer motor to which electrical power is connected by at least a pair ofinput leads. A resistor is connected in circuit with one of the inputpower terminals and the chassis and one terminal of the moisture sensingelectrodes is connected to the chassis. The control circuit assures safeoperating conditions of the dryer, even if the machine is not groundedby a grounding conductor. The circuit also provides safe operatingconditions for either way in which the power plug is inserted intotheelectrical outlet and also provides safe operating conditions if metalparts of the dryer become exposed.

Other objects, features and advantages of the present invention will bereadily apparent from the following detailed description of certainpreferred embodiments thereof taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the control circuitof this invention schematically with the cabinet of the dryer properlygrounded and the neutral power line connected to the timer motor;

FIG. 2 illustrates the control circuit of this invention with theneutral power line connected to the timer motor and the cabinet of thedryer not grounded;

FIG. 3 is a schematic view with the ungrounded power line connected tothe timer motor and with the cabinet of the dryer grounded;

FIG. 4 illustrates the control circuit with the ungrounded power lineconnected to the timer and motor and the cabinet of the dryer notgrounded; and

FIG. 5 illustrates a stationary bulkhead of a dryer 3,522,660 PatentedAug. 4, 1970 ice illustrating the moisture sensing electrodes of thedryer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the present inventionis generally applicable to dryers, an illustrative embodiment of atypical dryer in which the inventive subject matter would haveapplication is shown in FIG. 5 which shows electrodes 11 and 12 of asensor assembly 13. The electrdoes 11 and 12, respectively, comprise aplurality of elongated fingers 11a and 12a. An air blower (not shown)provides air to the dryer through the inlet supply opening 14 and afterthe air is passed through the fabric to dry it, it passes out the outletopening 16.

The dryness control of this invention is illustrated in FIGS. 1 through4. The circuit diagrams of all of the figures are similar and theydiffer only in the grounding connections and in the way the neutral andhot power lines have been connected to the dryer. For example, in eachof the schematic diagrams, timer motor 17 is illustrated and a siliconcontrol rectifier 18 is connected in parallel with the motor 17. Thegate electrode 19 of the silicon control rectifier 18 is connected to aneon lamp 21 which has its opposite side connected to a resistor R Theother side of resistor R is connected to the cathode of a diode 22. Theanode of diode 22 is connected to a resistor R which has its other sideconnected to moisture sensing electrode 11. The moisture sensingelectrode 12 is grounded to the chassis of the machine. The capacitor C;has one side connected to the anode of diode 22 and the other sideconnected to an input lead 23 of the control circuit. A resistor R isconnected between leads 23 and the chassis of the machine. The otherinput lead 24 is connected to a timer contact switch 26 which isconnected in circuit with the series resistor R The other side of theresistor R is connected to the second terminal of the timer motor 17 andto the cathode of the silicon controlled rectifier 18. A resistor R isconnected between the gate 19 and the cathode of the silicon controlledrectifier 18. A resistor R is connected from the cathode of the diode 22to the cathode of silicon controlled rectifier 18.

All of the portions of the control circuit illustrated in FIGS. 1through 4 up to this point are the same. The input leads 23 and 24 areconnected to an electrical plug which is inserted into a suitable powersocket during operation of the machine. The plug to which lines 23 and24 are connected may be inserted into the socket such that line 23 isconnected to the neutral line of the power socket and the line 24 isconnected to the ungrounded power lead. Alternatively, the plug to whichlines 23 and 24 are connected may be inserted into the power socket suchthat the line 23 is connected to the ungrounded power line L and thelead 24 is connected to the grounded neutral lead of the power supply.Dryers should be grounded by a grounding conductor which extends fromthe chassis of the dryer to a suitable ground point as for example awater pipe. FIGS. 1 through 4 illustrate the control circuit connectedto the power lines in various ways and with grounded and ungroundedconditions.

FIG. 1, for example, illustrates the input lead 23 connected to theneutral power line N and point Y and with a grounding connectorconnected from the chassis of the machine to an earth ground which isalso connected to the neutral power line N. This is the recommendeddesired installation and the dryer cabinet will act as a conductormaking connections which short out the resistor R When the neutral lineN is positive, the capacitor C will charge through timer switch 26,resistors R and R and rectifier diode 22. When wet fabric contactssensors 11 and 12, the DC voltage developed on capacitor C will be quitesmall and therefore the voltage between points C and D will reach thebreakdown voltage of neon 21. Neon 21 will fire and turn on the SCR 18and timer motor 17 will be shunted by a short circuit during half thetime. Timer motor 17 may be a shaded pole motor which will not operateon half-wave voltage and thus the timer motor 17 will not advance whenwet fabric bridges the sensor. As the fabric in the dryer becomes drierand presents a higher resistance across the sensors 11 and 12, thevoltage on capacitor C, will increase. When this voltage becomes so highthat the voltage from point C to point D is insufiicient to fire theneon 21, the timer motor 17 will begin to operate and run out toterminate the dryer cycle.

The resistor R is selected large enough to limit the current to protecta person touching sensors 13 from shock hazard. Resistors R R and R andcapacitor C are selected so that the difference between the peak of theAC line voltage minus the DC voltage across the capacitor C will exceedthe ionization voltage of the neon 21 over the full design range of theline voltage supplied to the machine.

FIG. 2 illustrates the supply lead 23 connected to the neutral line N ofthe power supply and the input lead 24 of the machine connected to theungrounded supply of the power supply L However, in this figure a groundlead has not been connected from the chassis of the machine to asuitable earth ground. Under these conditions the circuit of FIG. 2operates the same as that of FIG. 1 except that the resistor R has beenplaced in series with the sensor 13. This causes the DC level on thecapacitor C to be somewhat higher than in the circuit of FIG. 1.Alternatively, the required supply line voltage connected to leads N andL will need to be slightly higher than for the configuration shown inFIG. 1 to obtain the same operating conditions.

FIG. 3 illustrates the condition wherein input lead 24 has beenconnected to the neutral power lead and input lead 23 has been connectedto the ungrounded lead L The chassis of the machine has been connectedto an earth ground by suitable grounding conductor 27. In this situationthe capacitor C resistor R and sensor 13 are connected in series acrossthe line terminals N and L The capacitor C is selected so that its 60cycle impedance will be low with respect to resistor R and this causesnearly full line voltage to appear between points C and D when wetfabric bridges sensors 13. Therefore, when L is positive the neon 21will fire and the timer motor 17 will not operate. As the clothes becomedry and present a higher resistance to sensor 13, capacitor C willcharge through switch 26, resistors R and R and the diode rectifier 22.When this voltage becomes so high that the voltage from point C to pointD is insufiicient to fire the neon 21, the timer motor 17 will begin tooperate and run out to terminate the dryer cycle.

FIG. 4 is very similar to FIG. 3 except the grounding conductor 27 hasnot been connected. This circuit operates substantially the same as thecircuit of FIG. 2. The control circuit of this invention eliminatespossible shock hazard for both conditions of the power plug and alsoprovides protection even if the ground lead is not connected. R isselected large enough so that when wet clothes bridge sensors 13 thecurrent through the parallel combination of R and R is limited toprotect a person touching sensors 13 from shock hazard. Thus, theproblem of possible shock hazard at the exposed electrode is overcomeand, consistent performance is achieved regardless of machine groundingand of reversed line plug insertion.

If floating electrodes are used, such grounding paths may affect theperformance of a dryer. In accordance with the present invention asensor is used which has one electrode connected to chassis ground.Grounded structural parts therefore act as extensions of the sensor andtherefore have little or no affect on drying performance.

Although minor modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a clothes dryer having a chassis, a control circuit having a timermotor connected between a pair of input power leads, a controlledconduction device having a control terminal connected in circuit withsaid timer motor to render said timer motor inoperative when saidcontrolled conduction device is in one conduction state, a gatingcircuit for said controlled conduction device including a capacitor anda plurality of moisture sensing electrodes, the improvement comprisingconnecting said capacitor in series with a diode between one of saidpair of input power leads and said control terminal, connecting a firstresistance between said control terminal and the other of said pair ofinput power leads, connecting said plurality of moisture sensingelectrodes between said control terminal and said chassis with one ofsaid electrodes connected to said chassis, and connecting a secondresistor between said one of said pair of input power leads and saidchassis.

2. A control circuit according to claim 1 wherein said controlledconduction device is connected in parallel with said timer motor.

3. A control circuit according to claim 2 wherein said controlledconduction device is a silicon controlled rectifier.

4. A control circuit according to claim 2 comprising connecting a thirdresistor in series with said timer motor between the input power leads,and connecting a fourth resistor between said plurality of moisturesensing electrodes and said control terminal.

5. A control circuit according to claim 4 comprising connecting a fifthresistor in series with a neon gate between said diode and said controlterminal, and connecting a sixth resistor between said control terminaland the connection of said first resistance and the other of said inputpower leads.

6. A control circuit according to claim 5 wherein said controlledconduction device is a silicon controlled rectifier and said controlterminal is the gate electrode.

References Cited UNITED STATES PATENTS 3,286,363 11/1966 Grimshaw 34-533,343,272 9/1967 Ianke et a1. 34-45 3,404,466 10/1968 Reid 34-53 X JOHNJ. CAMBY, Primary Examiner U.S. Cl. X.R. 34-53

